This issue is extremely widespread and started yesterday. It's unclear what caused it as there was no software update or external event that we know of to explain it.
10.7 clients connecting to 10.6 server... GO > Connect to Server> (URL).... takes a very long time for the login to come up. Browsing to the server via bonjour (if possible network wise) works fine.
The *fix* is to remove from the user's prefs folder....
and then reboot the system.